The present invention relates to a kneader for kneading particulate or granular materials with optimum efficiency in accordance with the amount of the material.
An apparatus is known for kneading molding sand with agitating rolls which are shiftable in accordance with the quantity of the molding sand to vary the pressure on the sand and ensure an efficient kneading operation.
With reference to FIG. 5 showing the apparatus, agitating rolls 2' having a flat peripheral surface are supported on a pair of arms 23', the midportions of which are pivoted on a vertical shaft 22' to render the arms turnable upward or downward. A compression spring 33' is connected between the upper ends of the arms 23'. The vertical shaft 22' is coupled to an unillustrated motor.
When the motor is driven, the agitating rolls 2' revolve around the vertical shaft 22' and, at the same time, rotate on their own axes while being supported by the arms 23', whereby molding sand can be kneaded.
With an increase in the quantity of the molding sand, the agitating rolls 2' are forced upward, whereas the compression spring 33' restrains the rise of rolls 2' to prevent the reduction of the kneading efficiency.
However when kneading an increased amount of molding sand, the peripheral surface of each roll 2' is inclined giving rise to a tendency of the sand to escape outward, so that the spring 33' is unable to exert pressure on the sand effectively. When kneading a reduced amount of sand, the weight of the roll 2' acts on the sand at all times, and especially while the sand is being discharged from the apparatus, the roll under gravity acts on a thin layer of sand with a pressure higher than is appropriate, producing hard plate-like pieces which seriously impair the quality of the molding sand.
Furthermore since the agitating rolls 2' have a flat outer peripheral surface, the sand is liable to escape from the surface outwardly of the roll. As a result, the agitating rolls 2' fail to exert pressure on the sand effectively and to achieve high kneading efficiency.